The invention relates to a method of replacing old underground conduits, which involves initially laying bare the old conduit, without altering its course in the ground, and then removal thereof from the ground and drawing in a new conduit, and which claims the priority of German patent application 10 2006 043 772.1, the content of which is incorporated by reference.
Methods of this type are known; German Patent document 195 04 484 C1 describes a device for removing buried cables with the aid of a ring-shaped drill head moving over the cable and equipped with nozzles for a flushing liquid. Soil surrounding the cable or several cables is washed away with the assistance of the nozzles to thereby expose the cable which then can be pulled out from the ground. The device has an eccentric connection for a hollow rod assembly comprised of individual rod sections connected to one another. The hollow rod assembly meets two tasks; Firstly, it supplies the device with flushing liquid, and secondly, it propels the device between a starting pit on one hand and a destination pit on the other hand.
When the device has washed the conduit free and reached the destination pit, the exposed cable is pulled out of the created borehole and, after removal of the flushing device, a connection adapter is secured to the rod assembly for attachment of one or more conduits. These conduits are then pulled into the flushing borehole with the aid of the rod assembly in the direction of the starting pit.
A further multistage method for trenchless replacement of underground conduits is described in the German patent document 102 11 833 (GB patent document 2 386 767). This device is additionally equipped with a boring bit and a further tool on its rearward end. It lays bare the buried conduit in the described manner and permits the exposed conduit to be pulled out from the flushing borehole. The old conduit can hereby be connected with a new conduit in order to be able to execute in a single operating cycle the withdrawal of the old conduit and the pulling in of the new conduit. How and when the drill rods are removed from the flushing borehole is not described.